1. Field of the invention
This invention relates to a mechanism that prevents feeding of more than one sheet of paper, at one time, in the document feeder of an electrostatic copying machine or an electrostatic printing machine.
2. Description of the prior art
In general, in the document feeder of copying machines, in order to prevent the feeding of more than one sheet of paper at one time, there is a mechanism having paper-supply rollers and separation rollers with different coefficients of friction that are paired (Japanese Laid-Open Utility Model Application 58-69842) or a mechanism having paper-supply rollers with cut portions (Japanese Laid-Open Patent Application 58-181618).
This invention relates to an improved mechanism for preventing the feeding of more than one sheet of paper at one time, which mechanism has paper-supply rollers with cut portions. First, the connection of this invention to the prior art is explained using FIG. 3, which shows the diagram of an electrostatic copying machine.
On the upper surface of housing 1 of the copying machine, there is a place 2 on which the manuscript to be copied is placed, and an automatic document feeder 3 that supplies the documents one by one thereto and discharges them therefrom.
Inside housing 1, there is a movable optical system 4 for exposure and a photoreceptor drum 5. The piled-up manuscripts 16 in the manuscript stocker 301 are sent from the top of the pile by the pushing roller 302 and reach the resist roller 305, while paper-supply roller 303 and the separation roller 304 act in preventing more than one sheet from being fed at one time. At this point there is a temporary pause until the driving belt 306 sends the manuscript forward to a fixed position onto the transparent manuscript placement place 2.
Then, the lamp 401 of the movable optical system for exposure 4, the collimating reflector 402, and the first mirror 403 move at velocity V from the position shown in the figure by solid lines to that on the right of the figure shown by dotted lines The second mirror 404 and the third mirror 405 move at velocity 1/2V to the position shown by dotted line, in the same manner. Thus, scanning exposure takes place via the optical system 4.
At this time, the reflected light from the manuscript 16 that is illuminated by the manuscript illumination lamp 401 forms an image on photoreceptor drum 5 by means of reflections in the order of the first mirror 403, the second mirror 404, the third mirror 405, and the fourth mirror 407 via the lens 406. Upon completion of the scanning exposure in the above-mentioned way, the movable optical reflection system 4 returns again to its original position, and the manuscript 16 is ejected through the ejection route 14 to the manuscript ejection stand 15.
The photoreceptor drum 5, which rotates in the direction of the arrow, has already been charged uniformly with a certain electric polarity by the corona discharger 501. An electrostatic latent image is formed on the surface of the drum that corresponds to the above-mentioned manuscript by means of this exposure treatment.
The latent image is developed with toner via the well-known magnetic brush developer 9. Copy paper that has come from paper-supply cassette 7 or 8 passes through the space between the drum 5 and the transfer corona discharger 502 and that between the drum 5 and separator corona discharger 503, and this toner image is transferred to the copy paper. The paper with the transferred image is conveyed to the fusing means 11 by the discharge belt 10, where the toner image is fused by means of heat to the copy paper and discharged into discharge tray 13 by the discharge roller 12.
The toner left on photoreceptor drum 5 is cleaned by the cleaning apparatus 16.
If necessary, the paper stocker 6 can supply special papers such as postcards, OHP film, tracing paper, etc. The document feeder 3 for supplying papers in the stocker 301 can be used with the stocker 6. Rollers 601 and 602 are simple conveying rollers, which are used to adjust the timing thereof with the manuscript image via the resist roller 605.
The main parts of the automatic document feeder 3 are shown in FIG. 4. The rotatory power is transmitted to the driving shaft (paper-supply roller shaft) 308 of the paper-supply roller 303 and the driving shaft (separation roller shaft) 309 of the separation roller 304 for preventing the feeding of more than one sheet of paper via the power gear 307 from the power transmission apparatus (not shown). To the driving shaft 308 of the paper-supply roller 303, the power of the driving shaft 310 of the pushing roller 302 is transmitted by belt 311, which goes around these two shafts. There are fan-shaped cams 312 on the rotatory shaft 313, for the purpose of establishing the timing of the pushing roller 302. Gears 314, 315, and 316 are provided between the driving shaft 308 and the rotatory shaft 313.
The driving shaft 308 of the paper-supply rollers 303 and the rotatory shaft 313 of the timing cams 312 rotate at the same gear ratio.
The driving shaft 308 of paper-supply roller 303 passes through the swinging levers 320 These levers 320, which are for pushing roller 302, comprise the driving shaft 310 of pushing roller 302, the roller-supporting arms 318 that support weight 317 for balance, and the engaging arms 319 that engage with timing cams 312.
At the end of the engaging arm 319, there is an engaging step 321 that engages with the timing cam 312.
The paper-supply rollers 303 are made of some substance such as rubber or synthetic resin that has a relatively large coefficient of friction. The separation rollers 304 are made of a material with a relatively smaller coefficient of friction compared to the paper-supply rollers.
The paper-supply rollers 303 and the separation rollers 304 are, as shown in FIG. 6, designed so that the distance between their shafts is slightly smaller than the sum of their radii. Ordinarily, during the supplying of paper, manuscript 16 is supplied bent into a wave fashion.
As shown in FIG. 2, there is an indentation 322 n one part of the outer circumference of the paper-supply roller 303, so that when the manuscript 16 arrives at the resist roller 305 and the manuscript is conveyed in the downstream direction, the pressure of the paper-supply roller 303 against the manuscript 16 can be reduced. At this time, the manuscript 16 is sandwiched between the paper-supply roller 303 and the separation roller 304 so as to be flat (FIG. 7).
Next, the working of the above-mentioned document feeder 3 will be explained with reference to FIG. 5.
Document papers 1 6 are piled on the stocker 301, the working of which is the same as that of the paper stocker 6, on which copying paper is piled; below, both documents and copying paper shall be referred to simply as "paper."
The situation at the beginning of copying is shown in FIG. 5(a). The pushing roller 302 is lifted over the top of the paper 16 on top of the stocker 301. This pushing roller 302 is positioned on the top of the swinging level 320 that is connected to the timing cam 312.
Paper supply starts in this situation, with the fan-shaped timing cam 312 first rotating to the right and releasing the swinging lever 320. For that reason, the pushing roller 302 drops onto the top of the paper 16 on the stocker 301 and sends the topmost paper in the direction of the paper-supply roller 303 (FIG. 5(b)).
The paper-supply roller 303 works with the separation roller 304 rotating in the opposite direction from the direction in which the paper is being sent, so that the paper will be sent in the direction of the pair of resist rollers 305 while multiple feeding of paper will be prevented (FIG. 5(c)). The situation in FIG. 5(c) is the same as that in FIG. 6, seen from the end of the paper, wherein the paper-supply roller 303 works to strengthen the friction between this roller 303 and the paper 16.
Then, as the paper-supply roller 303 rotates once, the front edge of the paper 16 reaches the resist roller 305, and is stopped with a slight bent for slope compensation.
At this time, the swinging lever 320 is pushed up again by the timing cam 312, and the pushing roller 302 is pulled up from the top of the papers 16 on the stocker 301 (FIG. 5(d)).
When the slope compensation of the paper and the timing adjustment are complete, the resist roller 305 pushes the paper 16 in the downstream direction of paper conveyance. At this time, the indented section 322 of the paper-supply roller 303 in the situation shown in FIG. 5(d) faces the separation roller 304, so that the load that weighs upon the paper 16 when sandwiched therebetween will be decreased. This situation corresponds to that in FIG. 7; when seen from the end, the paper is completely flat. Thus, the paper 16 is quickly sent downstream in the direction of paper conveyance by the resist roller 305 without resistance.
When a paper-supply roller 303 with such an indentation in part 322 is used, the paper movement from the resist roller 305 downstream becomes smooth, there being only a light load on the paper. At the same time, since the load on the paper by the separation roller 304 has disappeared, the problem arises that the separation of multiple sheets of paper becomes unreliable.